The present invention relates to a novel thermoplastic resin composition. More specifically, the present invention relates to a thermoplastic resin composition which can markedly improve a thermal aging (or ageing) resistance of a thermoplastic resin when it is molded, a resin molded article obtained by molding the same, and a terminal product (resin molded product) containing this molded article.
2. Description of the Related Art
A resin molded article which is obtained by using a thermoplastic resin, and, for example, kneading and molding the same, has been used in many fields, for example, automobile parts such as a bumper product and an instrumental panel, electric parts such as a computer housing, and building products such as an insulation material.
When producing these resin molded articles and molded products thereof, kneading was hitherto conducted with heating. However, this procedure was problematic in a thermal aging (or ageing) resistance in view of occurrence of coloration, a decrease in a resin strength and the like. Accordingly, in order to prevent this, an antioxidant was added (refer to Antioxidant Handbook, Taiseisha, 1st edition, published Oct. 25, 1976).
In this case, phenolic, phosphorus-type, amine-type and sulfur-type antioxidants are added to prevent the coloration and the decrease in the resin strength. However, the dispersibility of the antioxidant is poor. Further, even when it is added in a large amount, an ability to prevent the coloration cannot be exhibited satisfactorily. Addition of the antioxidant in a large amount decreases the resin strength, and is economically disadvantageous.
There is another method using an additive which is ordinarily employed as a lubricant, such as a fatty acid, a fatty acid metal soap, for example, a fatty acid calcium salt, or a fatty acid amide. Nevertheless, this method cannot provide a sufficient dispersion effect, and the lubricant is liable to bleed out from a resin molded article. It is known that a condensate of polyglycerin and a hydroxycarboxylic acid polycondensate (polyester) is used to improve a thermal aging resistance (refer to Japanese Patent Kokai Publication No. JP-A-8-302,065). However, a satisfactory thermal aging resistance is not necessarily provided. Further, it is reported that a composition obtained by mixing a thermoplastic resin with a polyglycerin fatty acid ester along with an inorganic filler can improve an impact strength and a weatherability (refer to Japanese Patent Kokai Publication No. JP-A-4-202,429). However, no satisfactory improvement of the thermal aging resistance is provided either.
Still further, there are reported a thermally stable polyolefin composition comprising a polyolefin, an inorganic filler, a hindered phenolic antioxidant, a sulfur-type antioxidant and a fatty acid (lauric acid, palmitic acid, stearic acid or the like) ester of a neopentyl-type polyhydric alcohol (refer to Japanese Patent Kokoku Publication No. JP-B-61-46,015), a method in which a porous sheet is produced by stretching a sheet obtained by melt-molding a composition comprising a polyolefin resin, a filler and a dipentaerythritol ester (refer to Japanese Patent Kokoku Publication No. JP-B-7-5, 781), an inorganic filler for a synthetic resin which is formed by coating a fatty acid ester of a polyhydric alcohol with an inorganic compound powder (refer to Japanese Patent Kokai Publication No. JP-A-52-49,254), a plastic composition obtained by incorporating a carrier and a fatty acid polyol-type ester in a synthetic resin (refer to Japanese Patent Kokai Publication No. JP-A-52-144,048), a polyolefin resin composition containing a polyolefin resin, an inorganic powder and an ester formed by the reaction of a trihydric or tetrahydric fatty alcohol, a fatty acid and a fatty dibasic acid in approximately equivalent amounts (refer to Japanese Patent Kokai Publication No. JP-A-64-90,234). However, the thermal aging resistance is not necessarily improved satisfactorily.